The present invention relates to a separating device for a sheet-like member used in an electronic copying machine, a printer, a facsimile and the like, in particular to a separating device with a separating pawl for separating a sheet-like member from members to be separated, such as a photosensitive member, a fixing roller and other media such as an intermediate transfer member used in a multi-color development, by pawl.
When a toner image is transferred onto a sheet-like member, such as transfer paper, from a photosensitive member or an intermediate transfer member used in a multi-color development, in particular, when the photosensitive member having a large radius of curvature and the intermediate transfer member having a large radius of carvature or the sheet-like member having a small stiffness is used, the sheet-like member is wound around the photosensitive member or the intermediate transfer member due to an electrostatic attraction and the like.
The sheet-like member is also apt to be curled to a great extent by a heat in a fixation process so as to wind around fixing rollers, when the toner image transferred onto the sheet-like member is fixed on the sheet-like member by means of the fixing rollers.
Accordingly, separating pawls have been used at these places to be brought into contact with the photosensitive member, the intermediate transfer member and the fixing roller, whereby the separating pawls separate the sheet-like member from the photosensitive member, the intermediate transfer member and the fixing roller.
A large number of performances have been required for such the separating pawls.
At first, smoothness and sliding properties are required. If the separating pawl is poor in smoothness, a surface of the photosensitive member is scratched in contact with the separating pawl, and an electrostatic charge is not given to these scratched portions, resulting in the formation of white-striped noises in copied images. Moreover, these injured portions are filled with toners to interrupt the irradiation of light. Therefore, the surface potential does not decrease, resulting in the formation of black-striped noises in copied images. In particular, organic photosensitive members, which have been widely used in recent years, have exhibited remarkably such the problems due to the softness of the surface thereof.
The separating pawl for separating a sheet-like member from fixing rollers also wears a surface of the fixing rollers.
Then, it is required that a toner does not adhere to the separating pawl. If a toner particle adheres to the separating pawl, the adhered toner particles fall onto the sheet-like member in contact with the photosensitive member or the fixing roller, resulting in black spot-like noises in copied images. Moreover, the adhered toner particles are fused by heat generated by the friction of the photosensitive member with the separating pawl or by heat of the fixing rollers to fix onto a surface of the separating pawl. The fixation of toner particles causes the obstruction of the normal contact of the separating pawl with the photosensitive member or the fixing roller, resulting in the failure of the separation of the sheet-like member, such as transfer paper.
The adherence of toner particles to the separating pawl for separating the sheet-like member from the photosensitive member is observed outstandingly at high temperature and under high humid condition. Therefore, it is also required that the separating pawl is excellent in water repellancy.
Such the adherence is often observed when the surface of the photosensitive member is formed of an amorphous carbon layer. This reason is not necessarily clear, but it is thought that the amorphous carbon is very active to charge electrically the separating pawl. Therefore, toner particles are liable to adhere to the separating pawl electrostatically.
It is further required that the separating pawl is excellent in wear resistance. There is a problem as to wear resistance when the separating pawl is mainly composed of resin components.